Early life history of Nibea albiflora (Richardson) was studied morphologically and ecologically on the basis of morphology and distribution of the adult and the reproduction in Ariake Sound which is situated in the west part of Kyushu.
1) Morphology and distribution of the adult
Though morphological characters of N.albiflora distributed in Ariake Sound are almost in agreement with the discription of the fish reported, significant difference is recognized between ones from the sound and the ones from East China Sea where the fish is abundantly distributed in the ratio of interorbital length to head length.
The adults of N. albiflora move toward shallower waters of the northern innermost region or the eastern region of the sound in April and May, and
stay in the coastal area of 2〜5m in depth of low tidal level till autumn.T hey leave the area in October〜December. and are distributed in quite deep area .
of more than 30m in depth near the mouth of the sound in cold season . Morphological characters and distribution of the fish suggest that the fish of the species in this sound belongs to a population which spends most of the life
in the sound and does not leave away from the sound.
2) Spawning
Spawning of N. albzflora is mainly carried out in May and June in the
shallow coastal area of 2〜5m in depth of low tidal level, above all in the northern innermost area where the fish is abundantly distributed.Water - temperature of the spawning area in the season is 18〜29℃ , and the usual concentration of the sea water in the area in the season is more than 1 3.55‰ in chlorinity, in which concentration fertilization of egg of N.
albiflora is found to be successfully performed.
Spawning of the fish is carried out from three to seven o'clock in the afternoon, and the time the ovarian eggs attain to the maximum capacity of fertilization coincides with the spawning time.
3) Embryonic development and early morphological growth
Egg of N. albiflora is almost transparent, colorless and spherical in shape
and has a narrow perivitelline space and one oil globule which is about 0.17mm
in diameter. Mean and range of diameter of artificially fertilized eggs from
five parent -fishes are 0.76mm and 0.69〜0.83 mm respectively. Though effect ofsea water concentration on egg diameter is not great, there is a tendency that the higher is the concentration where the egg is fertilized, the smaller is the diameter of the egg.
Specific gravity of the egg changes according to that of the circumstance,
being 18.3〜19.6 in usual concentration of the spawning area 15〜18‰ Inchlorinity) at
24℃ of water - temperature.Embryonic development shown in Table 9 and Figure 19 is almost the same as common one observed on general pelagic fish egg. Hatching took place
37hr. 30min. at 19℃ and l5hr. 40min. at 29℃ after insemination.
Newly hatched larva from artificially fertilized egg is 1.5mm in total length and has 27 myomeres (8 + 19 = 27). By three days after hatching, opening of mouth, appearance of black pigments on the eyes, formation of pectoral fins and elongation of tail took place. As for chroniatophores on the body, mela- nophores, being in the dorsal part on the newly hatched larva, -generally shift to the body sides and the ventral margin, and assemble thickly on the sides and the ventral margin of middle part of the tail forming a characteristic band, while xanthophores are scattered throughout the most part of the body.
Morphological growth in post larval and prejuvenile stages (A. J. Mansueti and J. D. Hardy, Jr., 1967) observed on individuals collected with larval nets in the innermost region of the sound is as follows.
Larva of 2.8mm in body length has teeth, and one of 4.0mm is forming rays' of vertical fins. Individual of 6〜7 mm has complete rays on each fin and is
regarded to have attained to the prejuvenile stage. In prejuvenile of
7〜8 Intn,the area of body surface covered with melanophores begins to spread on the sides of the trunk, and in one of 15mm, scales begin to be formed. Individual
of 70〜80 mm in which most of the morphological changes have been acc opmlished and the typical striped pattern of the adult appears on the sides of
the body is regarded to have already attained to the juvenile stage.
Air - bladder is formed by three days after hatching, and its external ap-pearance forming two series of arborescent appendixes on the dorsal sides grows to be the same as that in the adult by the stage of 80mm in body length.
Muscles in body cavity which are connected to the airbladder and reportedly related to sound production are formed and begin to grow in the stage of 80mm. The fish begins to croak in juvenile stage of more than 120mm.
As for morphology of digestive organ, stomach is formed in the stage of yolk
absorption 2〜3mm in body length), intestine is convoluted in the stage of
4〜7mm, and the external appearance of the adult is provided by the stage of 9mm.
Larva and prejuvenile of N. albiflora are quite resemble to those of Argyrosomus argentatus which are abundantly distributed in the same area as the former and caught simultaneously. Post larva and prejuvenile of N. albiflora may be discriminated from those of A. argentatus by the differences that, in the former, a clucter of melanophores is located behind the anal fin base more anteriorly, that melanophores of the dody sides first appear on the position anterior to the dorsal fin, while those of A. argentatus appear beneath the fin, and that the clumps of melanophores on the body sides are obscurer. , In prejuvenile of more than 20mm and juvenile, there are distinct differences
that those of N. albiffora have larger eyes and higher body proportion.
According to relative growth examined about larvae, prejuveniles and
juve-niles, relative values of head and trunk lenght to body length, depth of tail to tail length, depth of head to head length, relation between head depth and body depth, upper jaw length to head length, and angle of upper jaw to body axis are far apart in larval stage from those of the adult, and get nearer to the adult's constants bya certain stage of growth, showing morphological change from typical character of the larva. Ratio of caudal fin length to total length is maximum in the stage of about 10mm in body length, showing typical character of young prejuvenile. Growth rate of the sound producing muscles shown as the ratio of the muscle weight in body weight increases in the stage of 120mm(male) and 140mm(female) in body length.
Relationship between body weight(Wg) and body length(Lcm) in young period
of 16〜150 mm in body length conforms to the following regression.
W= 0.0165L 3.010
Larvae of N. albiflora appear in the sound from May to August and attain
to 50〜180 mm in body length by the end of the first year. Modes of the body
length at age one and age two are about 170mm and 230mm respectively.
4) Ecology in egg and young period
As to the vertical distribution of eggs of N. albiflora, it is found that, in the water of higher specific gravity than that of the egg, eggs are more in the bottom layer during some period after the spawning, and after a while the number of eggs increases in the upper layer. This suggests that the spawning is carried out in the bottom layer, and in the water of higher specific gravity than that of the egg, eggs ascend gradually.
The eggs are mainly distributed in shallow waters of the innermost region, and rare in the middle area and the area near the mouth of the sound where the water is comparatively oceanic and deep.
Larvae and small prejuveniles are mainly distributed being densely assembled in some restricted coastal areas of the innermost region of the sound, and such a tendency is found that the larger the size of individual is, the shallower waters and the nearer to the coast it is distributed.
Prejuveniles and juveniles are seen in shallow water areas near the coast of the innermost region that are the mouth area of river, intertidal zone off the mouth of river, and zones just lower than low tidal level from June to Sep-tember, and in comparatively deep area of the region where the depth at low
tidal level is.2〜5 m from September to December. As for the body length com-position in each area, most of individuals in the mouth area of river are 6〜
20mm, ones in the intertidal zone and ones in the shallow waters near low tidal level, are 6〜60 mm and 6〜80 mm respectively, and ones in the com -paratively deep area are 11!〜150.
mm
These facts about occurrence and body length composition suggest that indi-viduals once recruited to shallow coastal area in larval stage move toward the deeper area with growth, and body length range of the group distributed in certain area varies dependently on depth of the area or distance from the shore.
As for the environmental condition in young stage, prejuveniles are distribu-ted in very wide ranges of water - temperature and sea water concentration,
being 22〜33℃ of water - temperature and 1〜17‰ in chlorinity, while the
adult lives in waters of 22〜29℃ and 16〜18‰
in chlorinity in warm
season
Stomach contents from individuals in each growth stage show that Copepoda,
Mysidacea, Gammaridae, Acetes japonicus, other Natantia, and small Brachyura
ドキュメント内
有明海産コイチの初期生活史に関する研究
(ページ 53-56)